Preliminary numerical investigation on the thermal feasibility of ground source heat pump system in civil defense facility

The persistently high cooling loads and stringent safety requirements in civil defense facility highlight the necessity for a safe and feasible thermal regulation system. This study aims to evaluate the thermal feasibility of ground source heat pump (GSHP) system with high concealment for application in the Zhushan civil defense facility located in Nanjing, China. First, A three-dimensional numerical model was developed, incorporating unsaturated porous soil, time-varying fluid flow rates, and environmental disturbances, to simulate the flow and heat transfer processes within the ground heat exchanger (GHE), as well as the heat transfer mechanisms of the grout and soil. Subsequently, this numerical model was coupled with the heat pump unit model through facility load, fluid temperature, and coefficient of performance (COP), enabling a comprehensive assessment of the system’s overall cooling efficiency. Finally, the load characteristics of facility, along with the energy consumption of system, fluid outlet temperature of GHE, T f,o , and COP of heat pump unit, COP hp , and system, COP sys , were investigated. Results indicate that the facility experiences consistently high cooling loads due to continuous heat gains from equipment operation and occupant metabolic activity. The system power consumption is dominated by the compressor, which accounts for approximately 80% of total usage, and exhibits a distinct seasonal pattern, characterized by a steady increase followed by a gradual decline, with peak usage occurring in August with highest cooling load. The average T f,o , COP hp , and COP sys is 24.51 °C, 5.35, and 4.42, respectively, with most data falling within narrow ranges: 23.75 °C-25.46 °C, 5.26-5.42, and 4.36-4.47. The minimum observed values are 18.78 °C, 5.17, and 4.22, while the maximums reach 26.43 °C, 5.78, and 4.71. The tight clustering of these values, along with a lower average, minimum, and maximum T f,o , as well as high average, minimum, and maximum COP hp and COP sys , demonstrates that the GSHP system operates under stable and efficient conditions and presents a thermally feasible solution for managing the persistently high cooling loads in civil defense facility. Distribution of fluid outlet temperature of GHE, T f,o , coefficient of performance for heat pump unit, COP hp , and coefficient of performance for system, COP sys , for ground source heat pump in civil defense facility with persistently high cooling loads.